A recurring problem in the repair of upholstered furniture is the degradation of the edges where the upholstery is tacked to the piece. Many upholsterers are not wood workers, so when removing old upholstery you never know what you will find. The picture below is of an Eastlake chair that has been recovered so many times that there is little left to drive tacks in to. You can see that the last man to upholster this chair drove tacks into the face of the rail in order to attach the fabric. I have seen all kinds of attempts to repair this type of damage, every thing from nailing wood to the frame to Bondo auto body filler.
The first and most difficult task is to remove all the old tacks in the edge of the rails. Most upholsterers will just leave many of the old and broken tacks in place. The remnant tacks will damage your edge tools when repairing the edge of the rail.
A rabbet is cut into the edge of the rail with a router plane and chisels.
Replacement wood glued into the rabbet.